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Annotation of 43BSDTahoe/etc/timed/cksum.tahoe.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1986 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution and use in source and binary forms are permitted
        !             6:  * provided that the above copyright notice and this paragraph are
        !             7:  * duplicated in all such forms and that any documentation,
        !             8:  * advertising materials, and other materials related to such
        !             9:  * distribution and use acknowledge that the software was developed
        !            10:  * by the University of California, Berkeley.  The name of the
        !            11:  * University may not be used to endorse or promote products derived
        !            12:  * from this software without specific prior written permission.
        !            13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            15:  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            16:  */
        !            17: 
        !            18: #ifndef lint
        !            19: static char sccsid[] = "@(#)cksum.tahoe.c      2.3 (Berkeley) 6/18/88";
        !            20: #endif /* not lint */
        !            21: 
        !            22: #include <sys/types.h>
        !            23: 
        !            24: /*
        !            25:  * Checksum routine for Internet Protocol family headers.
        !            26:  *
        !            27:  * This routine is very heavily used in the network
        !            28:  * code and should be modified for each CPU to be as fast as possible.
        !            29:  * 
        !            30:  * This implementation is TAHOE version.
        !            31:  */
        !            32: 
        !            33: #undef ADDCARRY
        !            34: #define ADDCARRY(sum) { \
        !            35:        if (sum & 0xffff0000) { \
        !            36:                sum &= 0xffff; \
        !            37:                sum++; \
        !            38:        } \
        !            39: }
        !            40: 
        !            41: in_cksum(addr, len)
        !            42:        register u_short *addr;
        !            43:        register int len;
        !            44: {
        !            45:        union word {
        !            46:                char    c[2];
        !            47:                u_short s;
        !            48:        } u;
        !            49:        register int sum = 0;
        !            50: 
        !            51:        while (len > 0) {
        !            52:                /*
        !            53:                 * add by words.
        !            54:                 */
        !            55:                while ((len -= 2) >= 0) {
        !            56:                        if ((int)addr & 0x1) {
        !            57:                                /* word is not aligned */
        !            58:                                u.c[0] = *(char *)addr;
        !            59:                                u.c[1] = *((char *)addr+1);
        !            60:                                sum += u.s;
        !            61:                                addr++;
        !            62:                        } else
        !            63:                                sum += *addr++;
        !            64:                        ADDCARRY(sum);
        !            65:                }
        !            66:                if (len == -1)
        !            67:                        /*
        !            68:                         * Odd number of bytes. 
        !            69:                         */
        !            70:                        u.c[0] = *(u_char *)addr;
        !            71:        }
        !            72:        if (len == -1) {
        !            73:                /* The last mbuf has odd # of bytes. Follow the
        !            74:                   standard (the odd byte is shifted left by 8 bits) */
        !            75:                u.c[1] = 0;
        !            76:                sum += u.s;
        !            77:                ADDCARRY(sum);
        !            78:        }
        !            79:        return (~sum & 0xffff);
        !            80: }

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